This invention relates to an endless track which is made of a reinforced rubber material with tread patterns having a first pitch and with longitudinally spaced and transversely disposed drive lugs, having a second pitch, different from the first pitch.
In the snowmobile industry, it has been a standard practice to have the drive lugs located exactly under the tread lug (traction lugs) which are both aligned with a composite stiffener which is used to reinforced the track. See for example U.S. Design Pat. No. 436,892 (Soucy and al). This arrangement of tread lug and composite stiffener give the drive lug enough strength to transmit power to the endless track. This leads to a number of drawbacks. One of them is that the drive lug pitch is driven by the outer tread pitch. Therefore, one has to compromise when designing a track since both elements accomplish different duties. The tread lugs cannot be too close together since the traction in snow would be reduced. After many years of development, the standard pitch in a snowmobile track has been set to the present 2.52 inches. At this pitch, although very functional, the noise and rolling resistance generated by the drive lugs are not optimized.
Environmental issues are a big concern in the snowmobile industry and reducing noise and rolling resistance is highly desirable for the comfort of the driver and of the people who are present near areas of snowmobile travel. The lowering of rolling resistance also lowers fuel consumption with the resulting lowering of combustion emissions.
One aspect of the present invention is to reduce substantially the noise generated from the endless track at all speeds and reduce rolling resistance (and thus fuel consumption) at low to medium speeds (0-70 mph) by having a drive lug pitch different than the tread pitch. It has been found that using a pitch exactly half the pitch of the tread is the best combination for overall snowmobile performance. Using this pitch length, the number of teeth engaged in the sprocket is doubled which reduces the unit impact force at engagement. On a test bench with that configuration, the noise reduction was between 1 to 5 dBa.
There is provided an endless track for a vehicle, the track having an endless body extending along a longitudinal axis and made of reinforced material, the body having a ground engaging outer side and an internal side, the ground-engaging outer side having a tread pattern over the entire length of the track and having a predetermined tread pitch length, the internal side provided with drive lugs repeated over the entire length of the track and having a predetermined drive pitch length, each drive lug having an engaging face laterally extending at an angle which is greater than 90xc2x0 or lesser than 90xc2x0 with respect to said longitudinal axis, wherein the drive pitch length differs from the tread pitch length.
These and other aspects and advantages of the present invention are described in or apparent from the following detailed description of a preferred embodiment mad in conjunction with the appended figures.